Among other useful applications of the steam engine are the steam plow, steam drill, steam dredge, steam press, and steam pump, of which latter the Blake, Knowles, and Worthington are representative types. [Illustration: FIG. 92.--THE SIX-CYLINDER QUADRUPLE EXPANSION ENGINES OF THE “DEUTSCHLAND,” 35,640 HORSE POWER.] The highest type of modern steam engines is to be found in the compound multiple-expansion engine, in which three or more cylinders of different diameters with corresponding pistons are so arranged that steam is made to act first upon the piston in the smallest cylinder at high pressure, and then discharging into the next larger cylinder, called the intermediate, acts expansively upon its piston, and thence, passing into the still larger low pressure cylinder, imparts its further expansive effect upon its piston. The fundamental principle of the compound engine dates back to the time of Watt, its first embodiment appearing in the Hornblower compound engine, as described in British patent No. 1,298, of 1781, but modern improvements have differentiated it into almost a new invention. A fine example is shown in Fig. 92, which represents the quadruple expansion engines of the “Deutschland,” the new steamer of the Hamburg-American Line. The two high pressure cylinders, however, do not appear in the illustration, being too high for the shops. They stand vertically, however, upon the two bed plates which appear at the top of the two low pressure cylinders. In each set of six cylinders the two low pressure cylinders are in the middle, the two high pressure cylinders immediately above them or arranged tandem, while at the forward end is the first intermediate cylinder, and at the after end is the second intermediate. The low pressure cylinders are 106 inches in diameter, the intermediate cylinders are 73.6 inches and 103.9 inches respectively, and the two high pressure cylinders are 30.6 inches, and the steam pressure is 225 pounds. Its improvements comprehend the systems of Schlick, patented in the United States November 23, 1897, No. 594,288 and 594,289, and Taylor, patented November 22, 1898, No. 614,674, which embody fine mathematical principles for balancing the momentum of the great masses of moving parts, so that the engine may run up to high speed without vibrations and damaging strains upon the hull. Mulhall gives the steam horse power of the world in 1895, not including war vessels, as follows: Stationary. Railway. Steamboat. Total. The World 11,340,000 32,235,000 12,005,000 55,580,000 United States 3,940,000 10,800,000 2,200,000 16,940,000 The increase in steam power in the United States has been from 3,500,000 horse power in 1860, to 16,940,000 horse power in 1895, or about five fold within thirty-five years.